The Pacific Ocean has seen a lot of early season tropical cyclone activity with a total of 11 cyclones forming before the end of June. This included some intense systems such as typhoons Higos, Maysak, Noul and Dolphin in the west Pacific and hurricanes Andres and Blanca in the east Pacific.

After a brief respite, early July has seen the development of further tropical cyclones across the Pacific Ocean triggered by a cyclical phenomenon known as the Madden-Julian Oscillation (MJO). The MJO is a pulse of cloud and rain which works its way eastwards around the globe in tropical regions. It often is seen to start in the Indian Ocean before crossing into the Pacific Ocean and occurs on a timescale of 30 to 60 days. The magnitude of the MJO will vary, but the event which moved into the western Pacific early in July has been very strong. A strong MJO produces conditions which are very conducive for tropical cyclone formation.

At the start of the month, the MJO event resulted firstly in the spinning up of twin cyclones – storms either side of the equator at the same longitude. Chan-hom formed in the north Pacific, whilst Raquel developed south of the equator. Raquel brought unseasonal heavy rain to the Solomon Islands before dissipating.

Left to right – Typhoons Linfa, Chan-hom and Nangka on 9 July 2015. Image courtesy of The National Institute of Informatics.

Chan-hom has continued to develop into a typhoon and has been joined by Typhoon Linfa to the west and Typhoon Nangka to the east as seen in the satellite image.

Linfa has just made landfall over southern China and is expected to bring stormy conditions to Hong Kong in the next day or so. Chan-hom is expected to pass close to the Japanese island of Okinawa before making landfall over eastern China. Nangka is currently over open ocean, but could affect south-western Japan in a few days time.

The tropical cyclone activity does not end there, however. As the MJO event moves east it is set to trigger more tropical cyclones in the central and eastern Pacific. Tropical Storm Ela has already formed and is set to pass just north of Hawaii in the next few days. There is also the indication from computer forecast models that one or two more tropical cyclones could develop in the eastern side of the Pacific in the next week.

The strong westerly winds associated with the latest MJO event are helping to enhance the developing El Niño by pushing warm waters in the western Pacific towards the east. A strong El Niño tends to promote tropical cyclone activity in the Pacific whilst suppressing it in the Atlantic.

Conditions are very unfavourable for the development of tropical cyclones in the Atlantic at present and we expect this to continue for much of the season. However, whilst activity is expected to be below average, this does not exclude the possible development of a few hurricanes in this region during the remainder of the year. Meanwhile, the Pacific is expected to see continued above average levels of tropical cyclone activity.

Official warnings for the latest tropical cyclones are produced by the Japan Meteorological Agency and the Central Pacific Hurricane Center. The Met Office routinely supplies predictions of cyclone tracks from its global forecast model to regional meteorological centres worldwide, which are used along with guidance from other models in the production of forecasts and guidance. We also provide updates on current tropical storms via @metofficestorms on Twitter.

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